A sulphur cement product generally refers to a product comprising at least sulphur and a particulate inorganic material. Examples of sulphur cement products are sulphur cement, sulphur mortar, sulphur concrete and sulphur-extended asphalt. Sulphur-extended asphalt is asphalt, i.e. typically aggregate with a binder that contains filler and a residual hydrocarbon fraction, wherein part of the binder has been replaced by sulphur, usually modified sulphur.
To improve the durability of the sulphur cement product, the sulphur may be modified in order to prevent allotropic transformation of the solid sulphur by the addition of a sulphur modifier in the sulphur cement product preparation process. Modified sulphur is typically prepared by mixing a portion of the sulphur with a sulphur modifier (also referred to as sulphur plasticizer). Such modifiers are known in the art. Examples of such modifiers are aliphatic or aromatic polysulphides or compounds that form polysulphides upon mixing with sulphur. Examples of compounds that form polysulphides are naphthalene or olefinic compounds such as 5-ethylidene-2-norbornene (ENB) or 5-vinyl-2-norbornene (VNB), dicyclopentadiene, limonene or styrene. Modifiers are usually added in an amount in the range of from 0.1 to 10 wt % based on the weight of sulphur. The effect of the sulphur modifier is the introduction of poly-sulphur in the bulk sulphur. The presence of poly-sulphur influences the crystallisation behaviour of the sulphur and increases the stability towards allotropic conformations. In WO2006134130 is disclosed a modified sulphur comprising either 5-ethylidene-2-norbornene and/or 5-vinyl-2-norbornene as modifier. Concrete prepared using the modified sulphur has a lower water absorption than unmodified sulfur concrete. The obtained compression strength is comparable to that of unmodified concrete.
In addition to using a sulphur modifier, it is known to use organosilane as a stabilising agent in sulphur cement products to improve water stability. Stabilizing agents inhibit or at least reduce the crystallisation of sulphur on the surface of particulate inorganic material. The addition of the stabilizing agent therefore results in a retarded sulphur crystallization. In U.S. Pat. No. 4,164,428 for example, a plasticized sulphur composition comprising at least 50% by weight of sulphur, a sulphur plasticizer, a finely divided particulate mineral suspending agent, and an organosilane stabilising agent is disclosed. It is mentioned that suitable organosilanes have the general molecular formula R—Si(OR′)3, wherein R′ is a low molecular weight alkyl group and R is an organic radical having at least one functional group, usually bonded to the silicon atom by a short alkyl chain. Gamma-mercaptopropyltrimethoxysilane is mentioned as a preferred organosilane. Disadvantages of the use of gamma-mercaptopropyltri-methoxysilane are that it is very toxic and that it has a very unpleasant smell.